Motor-control system



B. E. LENEHAN MOTOR CONTROL SYSTEM Fi1ed Nov .v-2, 1927 June 4, 1929.

INVENTOR Bernardf Lene/mn ATTOI'QNEY Patented June 4, 1929.

UNITED ;STATES BERNARD E. LENEHAN, Oi WILKDQ'SBUBG,

HOUSE ELECTRIC & MANUFACTURING VANIA.

PENNSYLVANIA, ASSIGNOB IO WESTING- OOMPANY, A CORPORATION OI 2mm- 1 V micron-common sYs'rEu.

Application filed November :7, 1927. Serial No. 230,400.

My invention relates to a motor control system and has particular reference to a motor utilizable for controlling an electrical measuring instrument.

My invention resides in apparatus associated with the control motors for graphic meters, regulators, remote indicators or the like. Such apparatus having reference to means for causing said motor to rotate in either direction at a constant speed in accordance with the variation of a measurable quantity.

My invention is an improvement in and is closely related to the subject-matter of Pat ent No; 1,580,457 that issued April 13, 1926, to Victor H. Todd, and was assigned to the vWestinghouse Electric & Manufacturing Company.

It is the purpose of my invention to improve the operating characteristics of a control motor of the type mentioned in the above patent and it is characteristic of my invention for such purpose that a control motor is adapted to operate on a smaller amount of energy, sparking is materially reduced across the relay contacts of the device and a more nearly perfect dynamic braking effect is produced. All of the above factors materially reduce the maintenance caused in the operation of such motors and in addition to the above it is characteristic of my invention that a control motor circuit constructed in accordance therewith is cheaper and more easily manufactured.

35 For a complete understanding of my invention both as to its purpose and construction reference may be had to the above men-- tioned patent.

Figure 1 of the accompanying drawing is a view partiallyin elevation and partially schematic of a preferred embodiment of my invention, and- Figure 2 is a diagrammatic view of the motor control circuit of my invention. I

Referring to the drawing a graphic wattmeter 1 isconnected in series and parallel circuit relation with an electrical circuit comprising conductors 3 and 4. The wattmeter 1 consists of the well known Kelvinbalance arrangement which includes a balance arm 5, a control motor 6,an arm 7 and aspring 8 connected in such manner that when the arm 5 is moved out of position of balance the'control motor 6 moves the arm 7 to turn the spring 8 so as to balance the position of the arm 5 in the usual and well known manner. p 1 Any suitable means maybe utilized for unbalancing the arm 5' in accordance with changes in a characteristic, as magnitude,of a quantity of the circuit comprisin the conductors 3 and 4. For example, t e arm 5 may be unbalanced in accordance with change in watt magnitude by means of stationary coils 9 connected in series circuit relation with conductor 4 that produce fluxes that react with coils 10 physically disposed on the balance arm 5 and'electrically connected in parallel circuit relation with the conductors 3 and 4 by conductors 11 and 12. An increase in the power traversing the conductors 3 and 4 causes the balance arm '5 to turn in one direction, for example, aclockwise direction, whereas a decrease in the power auses the arm 5 to move in the opposite elirection, i. e., counter-clockwise.

Any unbalance in the arm 5 is adapted to rotate the control motor 6 in a direction depending upon the direction of movement of the balance arm 5. To this end, a contact arm13 is mounted on the balancearm 5 to move between contacts 14 and 15. The con-- trol motor 6 drives a worm screw 16. The worm screw 16 -drives a pen carriage to the right or left depending upon the direction of rotation of the worm screw 16. The, pen carriage 17 cooperates with the arm 7 to move the lower end of the latter by means of a slot 18 in the arm 7 and apin 19 secured to the pen carriage 17. The pen carriage 17 carries an inking member 20 that makes a mark 21 on a paper chart 22 when the latter is moved downwardly by the rotation of spindles 22' that are actuated by the well known constant speed clocks or motor mechanisms (not shown) but well known to those skilled in the art.

The above described Kelvin balance ar-- rangement and graphic recording device is well known'an'd has been described in connection with my invention as being a preferred embodiment of a device in which a control motor circuit constructed in accordance with my invention is particularly. applicable.

My "nvention comprises a Wheatstone bridge network whose arms 23, 24, 25 and 26 each comprise a resistance element. The armature windingof motor 6 shunts a pair 24 and 25 of said arms. 'A second motor winding of motor ductors at junction 28 of a pair 24'and 25 of said arms. There is also provided an -arrangement for unbalancing saidnetwork in response to changes in a charactenstic of a quantity of the circuit'comprismg the conductors 3 and 4 which, in the examp e lllustrated, is watts. The motor winding 27 may be either the stationary or movab e wmdmg of the motor 6, but for purposes of llustration it will hereafter be referred to as the fieldmagnet-winding. The field-m et-w ndmg 27 comprises a circuit in aralle c1rcu1t relation with conductors 3 an 4 of the sugply cirbe cuit. Current is directed through t e fieldmagnet-winding 27 by a conductor 28a that is connected, for example, to the conductor 4 1 at 29 and to one terminal 30 of the field-magnet-winding 27. The opposite corner 31' of the Wheatstone bridge network is connected to conductor 3 at 32 by a conductor 33. The contact arm 13 is also joined to the point 31 andis preferably of the same potentlal but is shown in the drawing for purposes of 1llustr'ation as being connected therewith by a conductor 34. v

The motor 6 comprises the field-magnetwindin 27 and an armature windin connected y conductors 36 and 37 to points 38 and 39, respectively, that are of equal potential when the contact arm 13 is in a osition midway between the contact mem ers 14 and 15.

The field-magnet-winding 27 is preferably constantly energized by a current that flows through a path comprising the conductor 28a, the field-ma ct-winding 27, the resistors 24 and 25, an 25 and 26, and conductor 22. The sum of the resistance of the resistors 23 resistance of the resistors 25 and 26 in order that the current traversin the above mentioned path will divide at t e point 28 so that substantially half of the current traverses the resistors 24 and 23 and the other half traverses the resistors 25 and 26. The resistors 24 and 25 are also preferably of equal resistand- 24 is preferably substantially equal to the 6, when the contact arm 13 is in a position midway between the contacts 14 and 15.

However, when an increase of the power traversing the conductors 3 and 4 causes the balance arm 5 to move the contact arm 13 into contact with member 14, the resistor 23 is short-circuited by arelatively low resistance path, and the potential between the points 39 and 38 is unbalanced thereby causing a difference of potential across the terminals of the armature winding of motor 6. Such difference of potential is made sufiicient in value to energize the armature winding of motor b 6 m such manner that its reaction with the flux of the field-magnet-winding 25 produces a rotational torque of suflicient strength to ance so that no current traverses the armature d I winding is connected to the conjugate conturn the worm screw 16 thereby moving the pen carriage 17 and the arm 7.

The contact between the members 13 and 14 short-circuits the resistor 23 thereby producing a predetermined direction of rotation in the motor 6, while contact between the members 13 and 15 short circuits the resistor 26 thereby causing a rotation of the armature of vthe motor 6 in the opposite d1- rection.

The resistors 23, 24, 25 and .26 comprisin the arms of the Wheatstone bridge are pre erably non-inductive in order that there shall a minimum arcing of the rela contacts due to self-induction of circuits roken by said contacts. Heretofore, the field windings of a motor controlcircuit have been in the position now occupied by the resistors 24 and 25. In such control circuits when the arm of the prior art device corresponding with the arm 5 was in an extreme clockwise position a short-circuited path included such windings and the members corresponding to the members 13 and 14; accordingly, when the latter were moved apart, the self-induction of such windings tained in the gap between the contacts 13 and 14. Such arcs or sparking, arising because of self-induction, is reduced to a minimum in accordance with my invention by moving the field-magnetwinding 27 to a position outside of the short-circuiting network and making the arms 24 and 25of resistance and especially of non-inductive resistance.

Heretofore, as in the example mentioned above, where the arms 24 and25' constituted portions of the field windings of the motor,

the power consumption of the motor was relatively high because of the power factors of the separate portions of the winding which were wound on the same core were different when one of the resistors was short-circuited by the relay contacts. In such case, the windings being on the same core had a neutraliz- -mg effect on each other that required a relatively high current to be drawn from a circuit comprising the conductors 3 and 4 in orer to provlde sulficient torque in the arma-' ture winding of motor 6.

As pointed out in the patent referred to a ve, the resistors 23 and 26, when shortcircuited. provide a path of low resistance around the relay contact members when the latter are opened thereby ing the sparking between such members. This together with the non-inductive arm of the bridge provide a relay contactor having negligible sparking.

On alternating current particularly, a control circuit. constructed in accordance with my invention has inherently good dynamic raking. This is due to the fact that the currents traversing the field winding 27 and the armature windings 35 are more nearly in phase. Such dynamic braking is highly dematerially reduc-.

caused an arc to be mainsirable in order to stop the pen carriage 17 as soon as possible after the relay contacts are broken.

As pointedout above, the power factor of a control circuit constructed in accordance with my invention is very high by virtue of the fact that the field-magnetic-winding 27 carries a current of definite and determinable value and the inductive effect of prior control circuits have been eliminated by the use of non-inductive resistance in the circuit breaking portion of the device.

All of the above mentioned advantages combine to reduce maintenance costs to a minimum, and by virtue of the fact of the use of the resistors 24 and 25 the control circuit is readily subject to manufacture and test. Such manufacturing and testing is seen to be highly desirable, when it is pointed out thatin a control circuit constructed in accordance with my invention,the field-magnet-winding 27 may comprise any standard field and the resistors may comprise standard resistance elements. In prior devices, where the field windings were divided electrically and placed on the same core mechanically it was, of course, necessary to provide special windings that materially added to the cost of manufacture and test of the control motor.

To sum up the advantages of a control circuit constructed in accordance with my invention, as indicated above, it first of all has a relatively low power consumption; second,

there is a minimum sparking between the relay contacts because of the non-inductive bridge arm; third, the dynamic braking of the armature is improved by the higher power factor available, and fourth, the device is relatively simple to connect and test because of the use of standard field windings and standard resistors.

Various changes and modifications may be made within the spirit of my invention without departing from the scope thereof as set forth in the appended claim.

I claim as my invention:

In combination, a motor comprising coacting rotor and field windings, a source of electric power for'energizing said motor, and a circuit for controlling the energization of said motor from said source of electric power comprising a plurality of resistors of equal resistance connected in the form of a Wheatstone bridge, means connecting opposite corners of said bridge to said source of supply in series-circuit relation with said field winding, means connecting said rotor winding to the other opposite corners of said bridge, and

means, including a contactor, for connecting a conductmg path around one of sald res1stors.-

In testimony whereof, I have hereunto sub-' scri lped my name this 26th day'of October, 192

BERNARD E. LENEHAN. 

